L.W., you are not 'wrong' to use magnum primers with those powders. &nbsp;Generally the magnum primers yield the best results with slow powders. &nbsp;In fact, two of the powders that you list (H110, WW296) have a heavy deterrent coating and can be hard to ignite. &nbsp;I can't really comment on 2400 not having ever used it.

It is true that occasionally someone will get better results with standard primers. &nbsp;Generally speaking I would not expect this to be true unless using very heavy bullets (for the caliber) and a fairly small amount of powder. &nbsp;That is pretty well the case with the .357 loads that you may have seen - a 185 grain bullet is pretty heavy for .35 cal and 14-16 grains of powder is not a whole lot.

Personally I use the Fed. small pistol magnum primers with the aforementioned .357 load, mainly because I have a brick of them. &nbsp;I did try the Winchester small pistol (not magnum) primers and didn't see any great change. &nbsp;With the Fed's I get 2&quot; groups at 50 yards. &nbsp;Good enough..... &nbsp;The key point is, work up the load with the primers that you intend to use and don't switch without reducing the load and starting over. &nbsp;They can and do vary in strength a lot.

By the way, there are some 'standard' primers that are rated for both 'regular' and 'magnum' loadings. &nbsp;Winchester only makes one size of large pistol primer so that's what I use in my .45 Colt w/296. &nbsp;Even more confusing is that some people will recommend small rifle primers for high-pressure handgun rounds like the .357 and .38 Super.

Bottom line.... use what works best for you, if you want to experiment, back down your loads and work up. &nbsp;Same advice as any other component change.

By the way your choice of standard primers for Blue Dot is probably a good one. &nbsp;It is not so hard to ignite as the Ball or Spherical powders.

I was getting primer piercing before I reached case overloading. I donít know what prompted me to try CCI 450ís instead of the 400ís which I had been using, but I did. Presto! No more piercing! Interesting!? A primer that has a hotter ignition and yet withstands more pressure! Thatís when I decided that it was time to do a dissection of all primers concerned. The chart above shows my results.

By studying the numbers, one can readily see which primers in the small rifle sections will withstand heavy loads. Primer cup diameters are all similar and appear to follow a specification, but check out the cup thickness in the small rifle primers (Dimension &quot;A&quot;). It is obvious that the thicker cups will withstand more pressure. Large rifle primers all appear to have the same cup thickness, no matter what the type. (As a note of interest, small pistol primers are .017&quot; thick and large pistol primers are .020&quot; thick.)
If you are shooting a 22 Cooper, Hornet, or a Bee, the .020&quot; cup will perform admirably. But try using the .020&quot; cup in a 17 Remington and youíll pierce primers, even with moderate loads.

Considering that cup thickness varies in the small rifle primers, it is obvious that primer &quot;flatness&quot; cannot solely be used as a pressure indicator.

Another factor which determines the strength of a primer cup is the work hardened state of the brass used to make the primer cup. They are made with cartridge brass (70% copper, 30% zinc), which can vary from 46,000 psi, soft, to 76,000 psi tensile strength when fully hardened. Manufacturers specify to their brass suppliers the hardness of brass desired. I was not able to test primer hardness, but an educated guess says that a primer manufacturer would choose a harder brass in order to keep material thickness down and reduce costs.

I have not run into primer piercing with large rifle primers. They are all the same thickness and therefore are not subject to the same misapplication problems. Exceptions can be created if too fast a powder is used in a magnum type case. The
22 Cheetah is a primer piercer with fast powders as Barry and I found out!
What does all this mean to the reloader?

Cases that utilize small rifle primers and operate at moderate pressures(40,000 psi) should use CCI 400, Federal 200, Rem 6 1/2, or Win SR. Such cases include 22 CCM, 22 Hornet and the 218 Bee. These primers are also used in heavy handguns such as the 9mm., 357, etc. Other cases that use the small rifle primer can use the above primers only if moderate loads are used. Keep to the lower end of reloading recommendations.

With large rifle primers all being the same thickness, choose a primer that makes the most accurate group, is the shiniest, cheapest or whatever, as they all have similar pressure capabilities.

Hope this clears up some primer confusion. If you wnat more information about primers, priming compounds, or even how to make primers, the NRA sells an excellent book called &quot;Ammunition Making&quot; by George Frost . This book tells it like it is in the ammo making industry.
Any comments call: Jim at James Calhoon Mfg.: 406-395-4079.